1. Field of the Invention
This invention relates to a package for accommodating and preserving medical devices, medical containers such as blood bags, containers containing solution administration, medicines, transintestinal nutrient foodstuffs and other various articles directly or after accomodating other containers and to a method for the manufacture thereof. More particularly, this invention relates to a package incorporating a stably sealed part and to a method for the manufacture thereof.
2. Description of Prior Arts
Most packages used for accommodating and preserving various articles or substances as described above have their peripheral edges sealed by heating with hot metal dies, high-frequency induction heating or ultrasonic heating. The heat sealing of the peripheral edge of a given package is accomplished, for example as illustrated in FIG. 1, by interposing between a lower metal die 1 and a heat sealing upper metal die 2, a lower sheet 3 and an upper sheet 5 having a hot melt layer 4 superposed or deposited on the lower sheet 3 side surface thereof and placed on top of the lower sheet 3, and subsequently pressing the upper metal die 2 down against the lower metal die 1 thereby fusing the two sheets 3, 5 along the peripheral edges thereof. The heat sealing upper metal die 2 conventionally used for this heat sealing usually has a land or flat surface.
When the upper metal die 2 has a land of large width as illustrated in FIG. 1, however, a force of fixed magnitude used by the upper metal die 2 in pressing the sheets produces a small pressure per unit area because of the large surface area of the land. Consequently, the peripheral edge of a finished package is sealed with insufficient strength such that it will readily separate under the influence of some external force.
When the upper metal die 2 has a land of small width as illustrated in FIG. 2, since the land has a small surface area, the pressure exerted by the upper metal die 2 per unit area is large so that the peripheral edges of the lower sheet 3 and the upper sheet 5 are joined with ample strength. Because of the small area of contact, however, the overall sealing strength to be produced is not sufficient and, moreover, the thickness of the upper sheet 5 is decreased along the peripheral edge 6 thereof which is subjected to the heat sealing. Thus, the heat sealed edge of a finished package has poor resistance to impacts and is liable to separate when the package is subjected to a drop test. Since the hot melt material in a fused state finds no room in the metal dies for its escape, there is a possibility that some of the fused hot melt material will find its way between and beyond the external bounds of the upper sheet 5 and the lower sheet 3 and stick out in the form of burrs 7. In the case of the sheet 5 on the heat sealing upper metal die 2 side, the portions of the upper sheet 5 which hit against the peripheral corners of the heat sealing upper metal die 2 form thin weak portions 8 as illustrated in FIG. 3. In an extreme case, these portions 8 may sustain pinholes. The occurrence of burrs as in the former case entails a problem that such burrs impair the appearance of the finished package. The occurrence of thin weak portions occasionally accompanied by pinholes as in the latter case entails a more serious problem, in that the finished container becomes incapable of safely preserving its contents and suffers from ready separation of the upper sheet. When the package is intended for a medical device or a medicine and, therefore, is required to ensure perfect isolation of its interior from the ambient air, the problem involved in the latter case will prove to be a fatal defect. Particularly when the package contains a medical container such as a blood bag or gh transfusion bag or a medical device, it weights heavily in itself. The sealed portion of the package, therefore, is exposed to a fairly large amount of stress when the bottom thereof sags down or when the package is dropped onto a solid surface. At times, this stress may be so high as to inflict breakage to the sealed portion of the package.